1. Technical Field
The present disclosure relates to a control apparatus for a power transmission system including an automatic transmission that is able to provide different power transmission paths that transmit power of a driving force source to a drive wheel.
2. Description of Related Art
There is well known a control apparatus for a power transmission system including an automatic transmission in which one of a first power transmission path and a second power transmission path, which transmits power of a driving force source to a drive wheel, is selectively established. In a predetermined state of a vehicle where vehicle vibration occurs, the control apparatus reduces the vehicle vibration or noise resulting from the vehicle vibration by half-engaging an engagement device for establishing the second power transmission path while the first transmission path remains established. This is, for example, a vibration reduction system for a vehicle, described in Japanese Patent Application Publication No. 2008-14457 (JP 2008-14457 A). JP 2008-14457 A describes a technique for establishing a semi-interlock state by half-engaging an engagement device, which is different from an engagement device required to establish a current speed stage and is interlocked when engaged, at a predetermined torque capacity in order to reduce vehicle vibration caused by the torsional resonance of a driveline in a state where a lockup clutch is engaged.
Incidentally, in the technique described in JP 2008-14457 A, when the speed stage of the automatic transmission is a first speed stage or a second speed stage, the semi-interlock state is established by half-engaging a clutch for establishing a third speed stage or a fourth speed stage, which is a higher vehicle speed-side speed stage. In this case, drivability may deteriorate because load acts in a direction to reduce the input shaft rotation speed of the automatic transmission, that is, because torque internally circulates. That is, if the semi-interlock state is uniformly established in order to reduce vehicle vibration or noise, drivability may be deteriorated.